The German Patent DE 38 25 134 A1 discusses a fuel injector that includes an electromagnetic actuating element having a solenoid coil, having an internal pole and having an outer magnetic-circuit component and a movable valve-closure member that cooperates with a valve seat assigned to a valve-seat member. The injector is surrounded by a plastic coating, the plastic coating first and foremost extending in the axial direction, surrounding the fitting used as internal pole and the solenoid coil. At least in the area surrounding the solenoid coil, ferromagnetic fillers conducting magnetic lines of force are introduced in the plastic coating. In this respect, the fillers surround the solenoid coil in the circumferential direction. The fillers are pieces of metal reduced to fine grain and having soft-magnetic properties. The small metal particles embedded magnetically in the plastic have a more or less globular shape and are magnetically isolated individually, and thus have no metallic contact among themselves, so that no effective magnetic-field formation occurs. However, standing in the way of the positive aspect of a very high electrical resistance thereby resulting is also an extremely high magnetic resistance, that is reflected in a considerable power loss, and therefore determines the functional properties which are negative in the overall balance.
A fuel injector is also discussed in DE 103 32 348 A1, which has the feature of a relatively compact construction. In this valve, the magnetic circuit is formed by a solenoid coil, a fixed internal pole, a movable solenoid armature, as well as an outer magnetic-circuit component in the form of a magnetic cup. For a slender and compact construction of the valve, a plurality of thin-walled valve sleeves are employed, which are used both as fitting and as valve-seat support and guide section for the solenoid armature. The thin-walled non-magnetic sleeve running within the magnetic circuit forms an air gap, via which the magnetic lines of force pass over from the outer magnetic-circuit component to the solenoid armature and internal pole. A fuel injector of a comparable type of construction is shown again in FIG. 1, and is explained in greater detail below in order to better understand the present invention.
In addition, JP 2002-48031 A discusses a fuel injector which likewise features a thin-walled sleeve design approach, the deep-drawn valve sleeve extending over the entire length of the valve, and in the magnetic-circuit area, having a magnetic separation point, at which the otherwise martensitic structure is interrupted. This non-magnetic intermediate section is disposed at the level of the area of the working air gap between the solenoid armature and internal pole and in relation to the solenoid coil to such an extent that as effective a magnetic circuit as possible is created. Such a magnetic separation is also used to increase the DFR (dynamic flow range) compared to known valves having conventional electromagnetic circuits. However, such designs are then again associated with considerable additional costs in manufacturing. In addition, the introduction of such a magnetic separation having a non-magnetic sleeve section leads to a different geometrical design compared to valves without a magnetic separation.